Nucleic acid-antibody constructs and their use in antigen detection

ABSTRACT

A process for detecting the presence or absence of a specific nucleic acid sequence or antibody in a sample using an oligonucleotide to bind to the nucleic acid sequence or antibody to be detected, forming double-stranded nucleic acid sequence using the bound oligonucleotide in conjunction with another oligonucleotide or DNA synthesis, synthesizing RNA transcripts from the thus-formed double-stranded nucleic acid sequence, and detecting the existence of the RNA transcripts, and oligonucleotides and kits useful in carrying out such a process.

This is a divisional application of application Ser. No. 08/654,243filed May 28, 1996, U.S. Pat. No. 5,723,297 which was a divisionalapplication of Ser. No. 08/441,687, filed May 15, 1995 (now U.S. Pat.No. 5,573,914) which application was a continuation of Ser. No.08/226,940, filed Apr. 13, 1994, abandoned, which was a continuation ofSer. No. 08/756,600, filed Sep. 10, 1991, abandoned. U.S. applicationSer. No. is 08/654,243 is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to processes for detecting the presence orabsence of nucleic acid sequences and antibodies in samples andoligonucleotides and kits useful in carrying out such processes.

BACKGROUND OF THE INVENTION

The present invention involves processes to detect nucleic acidsequences and antibodies in samples by amplifying signals associatedwith the existence of such nucleic acid sequences and antibodies. Inparticular, an oligonucleotide sequence is bound to the nucleic acidsequence to be detected or, through a connector molecule, to an antibodyto be detected, and that oligonucleotide is used to form adouble-stranded nucleic acid sequence which is used to synthesizerelatively large quantities of RNA transcripts in a short period of timefor detection.

Many target and signal amplification techniques have been described inthe literature, but none of these techniques are believed to offer thecombination of specificity, simplicity, and speed of the presentinvention. Some of these various techniques are described below.

a) Polymerase Chain Reaction (PCR) PCR is described in Saiki et al.(1985), Science, 230 1350. PCR consists of repeated cycles of DNApolymerase generated primer extension reactions. The target DNA is heatdenatured and two oligonucleotides, which bracket the target sequence onopposite strands of the DNA to be amplified, are hybridized. Theseoligonucleotides become primers for use with DNA polymerase. The DNA iscopied by primer extension to make a second copy of both strands. Byrepeating the cycle of heat denaturation, primer hybridization andextension, the target DNA can be amplified a million fold or more inabout two to four hours. PCR is a molecular biology tool which must beused in conjunction with a detection technique to determine the resultsof amplification. The advantage of PCR is that it may increasesensitivity by amplifying the amount of target DNA by 1 million to 1billion fold in about 4 hours. The disadvantage is that contaminationmay result in false positive results (i.e., reduced specificity).

b) Transcription Amplification (TAS) TAS utilizes RNA transcription toamplify a DNA or RNA target and is described in Kwoh et al. (1989) Proc.Natl. Acad. Sci. USA 86, 1173. TAS uses two phases of amplification. Inphase 1 of TAS a duplex cDNA is formed containing an overhanging, singlestranded T7 transcription promoter by hybridizing a polynucleotide tothe target. The DNA is copied by reverse transcriptase into a duplexform. This is heat denatured and a primer for the opposite strand fromthat with the T7 region is hybridized. Using this primer, reversetranscriptase is again added to create a double stranded cDNA, which nowhas a double stranded (active) T7 polymerase binding site. T7 RNApolymerase transcribes the duplex to create a large quantity of singlestranded RNA. This is the completion of phase one of TAS. In phase 2,the primer is again used. This time it is hybridized to the new RNA andagain converted to duplex cDNA. The duplex is heat denatured and thecycle is continued as before. In contrast to PCR where two copies of thetarget are generated each cycle, the advantage of TAS is that between 10and 100 copies of each target molecule are produced with each cycle.This means that 10⁶ fold amplification can be achieved in only 4 to 6cycles, but this still takes 3-4 hours. The major disadvantage of TAS isthe number of enzymes addition steps and the heat denaturationrequirements.

c) Transcriptions Amplification (3SR) In a modification of TAS, known as3SR, enzymatic degradation of the RNA of the RNA/DNA heteroduplex isused instead of heat denaturation, as described in Guatelli et al.(1990) Proc. Natl. Acad. Sci. USA 87, 1874. RNAse H and all otherenzymes are added to the reaction and all steps occur at the sametemperature and without further reagent additions. Following thisprocess, amplification of 10⁶ to 10⁹ have been achieved in 1 hour at 42°C.

d) Ligation Amplification (LAR/LAS) Ligation amplification reaction orligation amplification system uses DNA ligase and four oligonucleotides,two per target strand. This technique is described in Wu, D. Y. andWallace, R. B. (1989) Genomics 4, 560. The oligonucleotides hybridize toadjacent sequences on the target DNA and are joined by the ligase. Thereaction is heat denatured and the cycle repeated. LAR suffers from thefact that the ligases can join the oligonucleotides even when they arenot hybridized to the target DNA. This results in a high background. Inaddition, LAR is not an efficient reaction and therefore currentlyrequires about five hours for each cycle. Thus, the amplification takesa couple of days.

e) O Beta RNA Replication In this technique, RNA replicase for thebacteriophage Q Beta, which replicates single stranded RNA, is used toamplify the target DNA, as described in Lizardi et al. (1988)Bio/Technology 6, 1197. First, the target DNA is hybridized to a primercontaining T7 promoter and a Q Beta 5' sequence region. Using thisprimer, reverse transcriptase generates a cDNA connecting the primer toits 5' end in the process. These two steps are similar to the TASprotocol. The resulting heteroduplex is heat denatured. Next, a secondprimer containing a Q Beta 3' sequence region is used to initiate asecond round of cDNA synthesis. This results in a double stranded DNAcontaining both 5' and 3' ends of the Q-Beta bacteriophage as well as anactive T7 RNA polymerase binding site. T7 RNA polymerase thentranscribes the ds-DNA into new RNA, which mimics the Q Beta virus.After extensive washing to remove any unhybridized probe, the new RNA iseluted from the target and replicated by Q Beta replicase. The latterreaction created 10⁷ amplification in 20 minutes. Significant backgroundmay be formed due to minute amounts of probe RNA that isnon-specifically retained during the reaction.

f) Chiron Signal Amplification The Chiron system, as described in Urdeaet al. (1987) Gene 61, 253, is extremely complex. It utilizes 12 captureoligonucleotide probes, 36 labeled oligonucleotides, 20 biotinylatedimmobilization probes that are cross-linked to 20 more enzyme labeledprobes. This massive conglomerate is built-up in a stepwise fashionrequiring numerous washing and reagent addition steps. Amplification islimited because there is no cycle. The probes simply form a largenetwork.

g) ImClone Signal Amplification ImClone utilizes a network conceptsimilar to Chiron, but the approach is completely different. The ImClonetechnique is described in Kohlbert et al. (1989) Mol and Cell Probes 3,59. ImClone first binds a single stranded M13 phage DNA containingtargeted probe. To this bound circular DNA is then hybridized about fiveadditional DNA fragments that only bind to one end and the other endhangs freely out in the solution. Another probe set is then hybridizedto the hanging portion of the previous set of probes. The latter set iseither labeled directly with an enzyme or it is biotinylated. If it isbiotinylated, then detection is via a streptavidin enzyme complex. Ineither case, detection is through an enzyme color reaction. Like theChiron method, ImClone relies on build-up of a large network. Becausethere is no repeated cycle, the reaction is not geometrically expanded,resulting in limited amplification.

BRIEF SUMMARY OF THE INVENTION

The present invention pertains to a process for detecting the presenceor absence of at least one specific nucleic acid sequence in a samplecontaining a nucleic acid or mixture of nucleic acids, which processcomprises immobilizing the specific nucleic acid sequence to bedetected, treating the sample with a first oligonucleotide sequenceunder hybridizing conditions such that a portion of the firstoligonucleotide sequence hybridizes to the specific nucleic acidsequence to be detected and a portion of the first oligonucleotidesequence does not hybridize to the specific nucleic acid sequence to bedetected, wherein the portion of the first oligonucleotide sequencewhich does not hybridize to the specific nucleic acid sequence to bedetected forms a RNA polymerase binding site and a nucleotide sequencecapable of transcribing RNA only when hybridized to a complementarynucleotide sequence, treating the sample to remove any of firstoligonucleotide sequence which is not hybridized to the specific nucleicacid sequence to be detected, treating the sample with a secondoligonucleotide sequence under hybridizing conditions such that thesecond oligonucleotide sequence hybridizes to the portion of the firstoligonucleotide sequence which does not hybridize to the specific acidsequence to be detected and forms an active RNA polymerase binding siteand nucleotide sequence capable of transcribing RNA, treating the samplewith RNA polymerase and nucleotide triphosphates such that thenucleotide sequence formed between a portion of the firstoligonucleotide sequence and a portion of the second oligonucleotidesequence results in the synthesis of RNA transcripts, and determiningwhether the RNA transcripts were synthesized.

Alternatively, the sample may be treated, after immobilization of thespecific nucleic acid sequence to be detected, with an oligonucleotidesequence under hybridizing conditions such that a portion of theoligonucleotide sequence hybridizes to the 3' end of the specificnucleic acid sequence to be detected which acts as a primer for theoligonucleotide sequence and a portion of the oligonucleotide sequencedoes not hybridize to the specific nucleic acid sequence to be detected,wherein the portion of the oligonucleotide sequence which does nothybridize to the specific nucleic acid sequence to be detected forms aRNA polymerase binding site and a nucleotide sequence capable oftranscribing RNA only when an extension product is synthesized from theprimer which is complementary to the oligonucleotide sequence, treatingthe sample with DNA polymerase, RNA polymerase, and nucleotidetriphosphates such that an extension product is synthesized from theprimer which is complementary to the oligonucleotide sequence to form anactive RNA polymerase binding site and nucleotide sequence capable oftranscribing RNA which results in the synthesis of RNA transcripts, anddetermining whether the RNA transcripts were synthesized.

The present invention is also applicable to the detection of thepresence or absence of antibodies through use of a "connector molecule."

It is an object of the present invention to provide a process for thedetection of nucleic acid sequences and antibodies in samples with ahigh degree of specificity and simplicity in a short period of time.

It is another object of the present invention to provide a process forthe detection of nucleic acid sequences and antibodies whereinoligonucleotide sequences act as primers, resulting in the repetitivesynthesis of additional transcripts.

It is a further object of the present invention to provideoligonucleotide sequences for use in efficiently and precisely detectingthe presence or absence of nucleic acid sequences and antibodies insamples.

It is yet another object of the present invention to provide kits usefulin quickly carrying out processes for the detection of the presence orabsence of nucleic acid sequences and antibodies in samples.

These and other objects and advantages of the present invention will beapparent from the description of the invention provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a preferred process of the present invention fordetecting nucleic acid sequences in a sample utilizing twooligonucleotides.

FIG. 2 depicts another preferred process of the present invention fordetecting nucleic acid sequences in a sample utilizing oneoligonucleotide and DNA synthesis.

FIG. 3 depicts a preferred process of the present invention fordetecting antibodies in a sample using two oligonucleotides and DNAsynthesis.

FIG. 4 depicts a process for reducing background by the use ofrestriction enzyme digestion.

FIG. 5 depicts another process for reducing background by denaturationof the specifically bound probe.

FIG. 6 depicts another process for detecting target nucleic acidsequences in a sample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is predicated on binding an oligonucleotide to thespecific nucleic acid sequence or antibody desired to be detected in asample, and then using that oligonucleotide to form a double-strandednucleic acid sequence, by using either another oligonucleotide or DNAsynthesis, and thereby synthesizing readily detectable quantities of RNAtranscripts.

The oligonucleotide sequence to be used in conjunction with the presentinvention comprises a portion which binds to a specific substance to bedetected in a sample and a portion which does not bind to said specificsubstance to be detected, wherein said portion of said oligonucleotidesequence which does not bind to said specific substance to be detectedforms a RNA polymerase binding site and a nucleotide sequence capable oftranscribing RNA when hybridized to a complementary nucleotide sequence.

In particular, the present invention involves a process for detectingthe presence or absence of at least one specific nucleic acid sequencein a sample containing a nucleic acid or mixture of nucleic acids, whichprocess comprises:

(a) immobilizing the specific nucleic acid sequence to be detected,

(b) treating the sample with a first oligonucleotide sequence underhybridizing conditions such that a portion of the first oligonucleotidesequence hybridizes to the specific nucleic acid sequence to be detectedand a portion of the first oligonucleotide sequence does not hybridizeto the specific nucleic acid sequence to be detected, wherein theportion of the first oligonucleotide sequence which does not hybridizeto the specific nucleic acid sequence to be detected forms a RNApolymerase binding site and a nucleotide sequence capable oftranscribing RNA when hybridized to a complementary nucleotide sequence,

(c) treating the sample to remove any of first oligonucleotide sequencewhich is not hybridized to the specific nucleic acid sequence to bedetected,

(d) treating the sample with a second oligonucleotide sequence underhybridizing conditions such that the second oligonucleotide sequencehybridizes to the portion of the first oligonucleotide sequence whichdoes not hybridize to the specific acid sequence to be detected andforms a RNA polymerase binding site and nucleotide sequence capable oftranscribing RNA,

(e) treating the sample with RNA polymerase and nucleotide triphosphatessuch that the nucleotide sequence formed between a portion of the firstoligonucleotide sequence and a portion of the second oligonucleotidesequence results in the synthesis of RNA transcripts, and

(f) determining whether the RNA transcripts were synthesized.

This process is preferably modified such that the sample at step (e) isfurther treated with the first oligonucleotide sequence capable ofhybridizing to the RNA transcripts and with DNA polymerase such that thefirst oligonucleotide sequence hybridizes to the RNA transcripts whichact as primers for synthesis of an extension nucleotide sequencecomplementary to the first oligonucleotide sequence to form a RNApolymerase binding site and a nucleotide sequence capable oftranscribing RNA which results in the synthesis of additional RNAtranscripts. More preferably, the step of treating the sample with thefirst oligonucleotide sequence and with DNA polymerase is repeated. TheRNA transcripts may also be virus fragments that are replicated throughuse of a RNA virus replicase.

Another preferred modification is to hybridize the first oligonucleotidesequence to the specific nucleic acid sequence to be detected at the 3'end of the first oligonucleotide sequence and then in treating thesample in step (c) to remove any of first oligonucleotide sequence whichis not hybridized to the specific nucleic acid sequence to be detectedincluding the treatment of the sample with a single strand specific3'-5' exonuclease such that the portion of the first oligonucleotidesequence which forms a RNA polymerase binding site when hybridized to acomplementary nucleotide sequence is cleaved from any of firstoligonucleotide sequence which is not hybridized to the specific nucleicacid sequence to be detected.

As an alternative, or in addition to these other modifications, thesample at step (c) may be further treated to separate the firstoligonucleotide sequence from the specific nucleic acid sequence to bedetected and the sample treated to remove any insoluble components. Thesample would, therefore, include primarily the (soluble) oligonucleotidesequence which had been bound to the specific nucleic acid sequence tobe detected in the sample, thereby further decreasing any background.The first oligonucleotide sequence may be separated from the specificnucleic acid sequence to be detected by any suitable means, such as bydenaturation.

Similarly, the sample at step (d) may be further treated to separate thefirst oligonucleotide sequence from the specific nucleic acid sequenceto be detected resulting in a soluble portion of the firstoligonucleotide sequence hybridized to the second oligonucleotidesequence forming a RNA polymerase binding site and nucleotide sequencecapable of transcribing RNA, with the sample thereafter being treated toremove any insoluble components. The first oligonucleotide sequence canbe separated from the specific nucleic acid sequence to be detected byany suitable means, e.g., through use of a restriction enzyme whichcleaves the portion of the first oligonucleotide sequence hybridized tothe specific nucleic acid sequence to be detected. Again, the samplewould include primarily the (soluble) oligonucleotide sequence which hadbeen bound to the specific nucleic acid sequence to be detected in thesample, thereby further decreasing any background.

The present inventive process may also be useful in amplifying thetargeted nucleic acid sequence, or a portion thereof, in the sample byselecting the first oligonucleotide sequence such that the portion ofthe first oligonucleotide sequence which hybridizes to the secondoligonucleotide sequence includes a nucleotide sequence identical to theportion of the first oligonucleotide sequence which hybridizes to thespecific nucleic acid sequence to be detected. In such an event, theportion of the first oligonucleotide sequence which hybridizes to thesecond oligonucleotide sequence is preferably identical to the portionof the first oligonucleotide sequence which hybridizes to the specificnucleic acid sequence to be detected.

An alternative to using a second oligonucleotide to hybridize to thefirst oligonucleotide to form a double-stranded nucleic acid sequencecapable of synthesizing RNA transcripts is to use the target sequence ofthe specific nucleic acid sequence to be detected in a sample as aprimer, in conjunction with DNA synthesis, to prepare the complementarynucleotides to yield the double-stranded nucleic acid sequence capableof synthesizing RNA transcripts. Such a process for detecting thepresence or absence of at least one specific nucleic acid sequence in asample containing a nucleic acid or mixture of nucleic acids comprises:

(a) immobilizing the specific nucleic acid sequence to be detected,

(b) treating the sample with an oligonucleotide sequence underhybridizing conditions such that a portion of the oligonucleotidesequence hybridizes to the 3' end of the specific nucleic acid sequenceto be detected which acts as a primer for the oligonucleotide sequenceand a portion of the oligonucleotide sequence does not hybridize to thespecific nucleic acid sequence to be detected, wherein the portion ofthe oligonucleotide sequence which does not hybridize to the specificnucleic acid sequence to be detected forms a RNA polymerase binding siteand a nucleotide sequence capable of transcribing RNA when an extensionproduct is synthesized from the primer which is complementary to theoligonucleotide sequence,

(c) treating the sample with DNA polymerase, RNA polymerase, andnucleotide triphosphates such that an extension product is synthesizedfrom the primer which is complementary to the oligonucleotide sequenceto form a RNA polymerase binding site and nucleotide sequence capable oftranscribing RNA which results in the synthesis of RNA transcripts, and

(d) determining whether the RNA transcripts were synthesized.

In a fashion similar to the present inventive process involving thesecond oligonucleotide, the sample at step (c) can be further treatedwith the oligonucleotide sequence capable of hybridizing to the RNAtranscripts and with DNA polymerase such that the oligonucleotidesequence hybridizes to the RNA transcripts which act as primers forsynthesis of an extension nucleotide sequence complementary to theoligonucleotide sequence to form a RNA polymerase binding site and anucleotide sequence capable of transcribing RNA which results in thesynthesis of additional RNA transcripts. Also, the step of treating thesample with the oligonucleotide sequence and with DNA polymerase may berepeated, and the RNA transcripts may be virus fragments which arereplicated through use of a RNA virus replicase.

The present inventive process also has applicability to the detection ofantibodies in samples. Specifically, the present inventive process fordetecting the presence or absence of at least one specific antibody in asample containing an antibody or mixture of antibodies comprises:

(a) immobilizing either the specific antibody to be detected in thesample or an antigen which binds to the specific antibody to bedetected,

(b) contacting the sample with an antigen which binds to the antibody toform an antibody-antigen complex which is immobilized,

(c) treating the sample to remove any of the antibody or the antigenwhich are not bound,

(d) treating the sample with a first oligonucleotide sequence such thata portion of the first oligonucleotide sequence binds to theantibody-antigen complex and a portion of the first oligonucleotidesequence does not bind to the antibody-antigen complex, wherein theportion of the first oligonucleotide sequence which does not bind to theantibody-antigen complex forms a RNA polymerase binding site and anucleotide sequence capable of transcribing RNA when hybridized to acomplementary nucleotide sequence,

(e) treating the sample to remove any of first oligonucleotide sequencewhich is not bound to the antibody-antigen complex,

(f) treating the sample with a second oligonucleotide sequence underhybridizing conditions such that the second oligonucleotide sequencehybridizes to the portion of the first oligonucleotide sequence whichdoes not bind to the antibody-antigen complex and forms a RNA polymerasebinding site and nucleotide sequence capable of transcribing RNA,

(g) treating the sample with RNA polymerase and nucleotide triphosphatessuch that the nucleotide sequence formed between a portion of the firstoligonucleotide sequence and a portion of the second oligonucleotidesequence results in the synthesis of RNA transcripts, and

(h) determining whether the RNA transcripts were synthesized.

As with the detection of nucleic acid sequences, the sample,specifically at step (g), can be further treated with the firstoligonucleotide sequence capable of hybridizing to the RNA transcriptsand with DNA polymerase such that the first oligonucleotide sequencehybridizes to the RNA transcripts which act as primers for synthesis ofan extension nucleotide sequence complementary to the firstoligonucleotide sequence to form a RNA polymerase binding site and anucleotide sequence capable of transcribing RNA which results in thesynthesis of additional RNA transcripts. The step of treating the samplewith the first oligonucleotide sequence and with DNA polymerase may, ofcourse, be repeated, and the RNA transcripts may be virus fragmentswhich are replicated through use of a RNA virus replicase.

While the first oligonucleotide may bind to the antibody in any suitablemanner, preferably the first oligonucleotide sequence is biotinylatedand binds to the antibody-antigen complex through astreptavidin-complexed molecule.

In addition, the second oligonucleotide sequence may act as a primer forthe first oligonucleotide sequence and the RNA polymerase binding siteand nucleotide sequence capable of transcribing RNA are formed by theaddition of DNA polymerase to the sample such that an extension productis synthesized from the primer which is complementary to the firstoligonucleotide sequence.

As is apparent from the discussion of the present invention in terms ofthe process of detecting nucleic acid sequences and antibodies insamples, the present invention involves the use of an oligonucleotidesequence comprising a portion which binds to a specific substance to bedetected in a sample and a portion which does not bind to the specificsubstance to be detected, wherein the portion of the oligonucleotidesequence which does not bind to the specific substance to be detectedforms a RNA polymerase binding site and a nucleotide sequence capable oftranscribing RNA when hybridized to a complementary nucleotide sequenceor when synthesized from a primer.

Kits for use in conjunction with the present invention in detecting thepresence or absence of at least one specific substance in a sample canbe devised which utilize such a first oligonucleotide sequence, alongwith a second oligonucleotide sequence which hybridizes with the portionof the first oligonucleotide sequence which does not hybridize to thespecific acid sequence to be detected and forms a RNA polymerase bindingsite and nucleotide sequence capable of transcribing RNA, RNApolymerase, nucleotide triphosphates, and a means for determining thepresence of RNA transcripts synthesized from the nucleotide sequencecapable of transcribing RNA. Alternatively such a kit for detecting thepresence or absence of at least one specific substance in a sample maycomprise a first oligonucleotide sequence as described above, DNApolymerase, RNA polymerase, nucleotide triphosphates, and a means fordetermining the presence of RNA transcripts synthesized from thenucleotide sequence capable of transcribing RNA.

The present invention may be further understood by reference to thefollowing illustrative examples.

EXAMPLES Example 1

Geometric signal amplification occurs via two stages. In the firstphase, Probe A, a portion of which is complementary to the target,hybridizes to the target. Attached to Probe A is a single stranded(inactive) RNA polymerase binding site. Next, another single strandedDNA, Probe B, hybridizes to the already captured Probe A. The secondhybridization converts the inactive RNA polymerase binding site to adouble stranded (active) form (FIG. 1). RNA polymerase, such as T7 orSP6 that require double stranded RNA polymerase binding sites forbinding, transcribes from the completed amplifier in a linear reaction.This is expected to generate between 10 and 1,000 times more RNA thanthere was original target. The actual quantity depends on how muchoriginal target there is and the concentrations of the nucleotidetriphosphates added to the mixture, as well as the reaction time.

In the second phase of the process, the new RNA transcripts hybridize toadditional Probe A, already present in the reaction mixture. The newlycreated transcripts are then utilized as primers for DNA synthesis torecreated the double stranded RNA polymerase binding site. The newbinding site can then start the whole cycle over again. Thus, thereaction becomes geometric.

The advantage of this approach is that it produces a geometric increasein the signal. This approach does not directly amplify the target, andtherefore, is good for diagnostic purposes.

A suitable procedure for carrying out this technique, therefore,involves the following process steps:

1) Immobilize target to a solid phase, via capture or membrane binding.

2) Hybridize Probe A to target. Wash away excess probe.

3) Hybridize Probe B to Probe A, thereby creating a double stranded RNApolymerase binding site. Wash away excess probe.

4) Add additional Probe A, double strand specific RNA polymerase, DNAdependent DNA Polymerase capable of using RNA primers (such as T7 DNApolymerase or E. Coli Pol 1), NTP's, dNTP's, reaction buffer forpolymerases, and biotinylated NTP as label (other label alternatives arepossible).

5) Transcribe from the double stranded RNA polymerase binding sitecreated by the hybridization of Probe A to Probe B.

6) Hybridize transcripts to excess Probe A.

7) Synthesize new DNA using RNA primer to create new double stranded DNAcontaining a new double stranded RNA polymerase binding site.

8) The geometric cycle is formed by steps 4-6.

Example 2

Example 2 is a variation of Example 1. The variation occurs in thesecondary amplifier reaction. The first phase reaction creates thedouble stranded RNA polymerase binding site and is transcribed as inExample 1. Inside the RNA transcript are the start and end sequences ofa single strand RNA virus, such as Q Beta. Thus, the first transcriptionreaction creates an internal RNA virus fragment which can then bereplicated by an RNA dependent RNA polymerase (a replicase). There are anumber of different RNA virus replicases that could be utilized for thistype of reaction. There is a primary transcription reaction followed bya secondary amplification from these new transcripts. There is nocycling back to start the reaction over again.

The advantage of this method, similar to Example 1, is a large signalamplification. There are only two hybridization steps, followed by therest of the transcription and replication steps being automatic. Such anamplification scheme may yield a billion fold amplification in only 20minutes or so.

An illustrative procedure for carrying out this technique involves thefollowing process steps:

1) Immobilize target to a solid phase, via capture or membrane binding.

2) Hybridize Probe A to target, wash away excess probe.

3) Hybridize Probe B (primary amplifier) to Probe A, thereby creating adouble stranded double strand specific RNA polymerase binding site, washaway excess probe.

4) Add double strand specific RNA polymerase, Q Beta Replicase, NTP's,Reaction buffer for polymerases, and biotinylated NTP as label (otherlabel alternatives are possible).

5) Transcribe from the double stranded RNA polymerase binding created bythe hybridization of Probe A to Probe B.

6) Replicate the internal portion of the newly transcribed RNA virion.

7) The geometric cycle is from steps 4 and 5.

Example 3

The advantage of this method is in its resistance to backgroundamplification from non-specific binding. The RNA polymerase binding sitecannot be created without having the probe bound to target. This alsopermits the addition of all reagents in a single step. Some compromisesmay be necessary for all reaction conditions, but the polymerases haverelatively similar reaction conditions.

This method has some limitations in the nature of the target moleculesthat are utilizable. The targets must have a 3'OH that can be used as aprimer for the DNA synthesis reaction. This makes the reaction ideal forlinear viruses like HIV and HPV, or for linearized molecules throughrestriction enzyme cutting or DNA shearing.

The procedure for carrying out this technique is as follows:

1) Add Probe A, DNA dependent DNA polymerase, such as T7 or E, coli Pol1, double strand binding site specific RNA polymerase, dNTP's, NTP's,and reaction buffer, and labeled NTP.

2) Hybridize Probe A to target with a 3' end, such that the 3'OH bindsto the probe region and is not dangling. No removal of the originalprobe is necessary and this probe is utilized subsequently in step 5.

3) Using the 3'OH and DNA dependent DNA polymerase, synthesize theremaining portion of the complementary strand of Probe A. This willcreate a double stranded RNA polymerase binding site. Transcribe usingRNA polymerase.

4) The transcripts hybridize to excess Probe A remaining after step 2.

5) Using this newly transcribed RNA as a primer, synthesize new doublestranded DNA and thereby recreate the double stranded RNA polymerasebinding site.

6) The geometric cycle is formed by steps 3-5.

Example 4

Background is a constant problem in amplification as well as DNA probebased detection assays. There are other signal amplifying reactions,which have been described, such as those developed by ImClone andChiron; but these do not address non-specific binding. Chiron'smethodology is excessively complicated and difficult to control. Theseother methods do not address the lack of specificity due to non-specificbinding, which results in high background. Any non-specifically boundprobe can be built into a large signal. From the practical standpoint,it appears that these approaches work moderately well, but have limitedamplification and may give false positives due to non-specificbackground. The present inventive process is inherently less prone tofalse signals due to non-specific binding and, in addition, can bemodified to include novel methods of background removal and two of theseare shown below.

The approach of the present invention is to limit or preventnon-specific binding from being able to be amplified. The methodillustrated in Example 3 is the most resistant to false signals becausethe amplification has a near absolute dependence on the probe's bindingto the target. The DNA synthesis step cannot take place unless the probeis bound to the target and there must be a 3'OH available.

The specificity of the technique of Example 1 is in the formation of theRNA polymerase binding site. Since double stranded DNA is required fortranscription, Probe A does not permit transcription by itself. In theprocedure, Probe A is hybridized to the target and excess is washedaway. Then Probe B is hybridized to the Probe A/target complex to allowtranscription to begin. Thus, no transcription can occur unless Probe Bbinds to Probe A.

It is possible for Probe A to bind non-specifically to the solid phaseand therefore, Probe B potentially could bind to this non-specificallybound Probe A and transcription could take place. However, transcriptionshould be limited because of the mechanism of non-specific binding ofProbe A to the solid phase. If the non-specific binding occurs only atthe 3' end of the probe, then hybridization of Probe B would not beimpeded, and transcription would occur. However, if non-specific bindingoccurs at multiple points along Probe A as expected, then hybridizationof Probe B would result in regions of single stranded DNa in the hybridat the sites where Probe A is bound to the solid phase. These singlestranded regions would terminate transcription prematurely or preventtranscription altogether. Reduction of the length of the RNA PrimerBinding Region to a small portion of the 5' end limits the capability ofthe run-off RNA transcripts to hybridize to the RNA Primer BindingRegion and initiate DNA synthesis. By making the RNA Primer BindingRegion small, only long transcripts will be able to hybridize. Theresult is termination of the cycling reaction due to failure of the DNAsynthesis to occur.

An alternative method for background reduction involves using 3'-5'exonuclease. Some exonucleases are single strand specific. They act bycleaving nucleotides from the 3' end, and, thus, are called 3'-5'exonucleases. The probe in Examples 1-3 can be used with the RNApolymerase binding site at the 3' end of Probe A to take advantage ofsingle strand specific 3'-5' exonuclease activity, such as Exonuclease 1of E. coli. After hybridization of Probe A to the target and washingaway the excess probe, the 3'-5' exonuclease is added to the reactionmixture. If the probe is bound to the target, then the RNA polymerasebinding site will be double stranded and protected from the action of3'-5' exonuclease. Wherever the probe non-specifically binds to amembrane or capture probe, the RNA polymerase binding (RPB) site will besingle stranded and accessible to the exonuclease. Furthermore, the RNApolymerase binding site will be near the 3' end of the probe so thatonly limited exonuclease activity will be required to destroy the RPBsite.

Example 5

The present inventive problems can also be utilized to increase thedetection of antibody reactions. The method applies to standard ELISAtype reactions in which antigen to which serum antibody binds is coatedon a microtiter plate. It also works equally well with antigen captureassays in which a primary antibody to which antigen binds is coated on amicrotiter plate (see FIG. 3).

The key is a connecting molecule, which links the serum antibody orantigen to the DNA probe amplifying system. The "connector molecule" maybe any suitable substance which will enable the oligonucleotide probe ofthe present invention to bind to the specific antibody to be detailed.Preferably, this molecule is another antibody that complexed tostreptavidin. Streptavidin is the linker through which a biotinylatedProbe A binds. The remainder of the amplification system is essentiallythe same as described in Example 1.

Example 6

This is an example of how the Signal Amplification scheme might be usedin an actual diagnostic test format. The example is shown for thetechnique set out in Example 1. It is assumed that the target is in verysmall quantity; otherwise the signal amplification technology would notbe used. The steps below indicate the basic application of signalamplification to a test format in a microtiter plate with a nylon ornitrocellulose filter forming the bottom of the well. In this format,the FITC becomes incorporated into newly synthesized RNA. Residualunincorporated nucleotide is removed to permit reading fluorescencewithout interference by binding the RNA to a filter and washing away theexcess unincorporated NTP. The numbers in parentheses are estimates ofthe time allowed per step. The total time for sample processing isestimated at 1.5 hours to 4.25 hours.

1) Lyse cells in Lysis Solution containing guanidinium thiocyanate andSDS; filter to bind DNA/RNA. (5')

2) Add Probe A (Primary Amplifier) and hybridize. (15'-60')

3) Wash away excess Probe A. (5'-15')

4) Add Probe B and Hybridize. (15'-60')

5) Wash away excess Probe B. (5'-15')

6) Add RNA Polymerase, DNA Polymerase, Probe A, FITC-labeled NTP,Transcribe, rehybridize, synthesize, repeat cycle. (30'-60')

7) Transfer solution to a new well and filter reaction through membraneto bind newly synthesized RNA. (5'-15')

8) Wash away excess unincorporated FITC-NTP. (5'-15')

9) Read residual fluorescence in well. (10')

Example 7

The following scheme is shown for the technique set out in Example 3.Only steps 6-9 are different from Example 6 above. In this format, theRNA is double labeled with both biotin for binding to the streptavidincoated plates and with FITC for reading the fluorescence. The excessFITC is removed by washing the plate after capture to permit readingonly the incorporated fluorescence. A limited quantity of biotinylatedNTP may be used to avoid competing with the biotin labeled RNA. Thetotal time is 1.75 hours to 5 hours.

6) Add RNA Polymerase, DNA Polymerase, Probe A, FITC-labeled NTP,Biotinylated NTP, Transcribe, rehybridize, synthesize, repeat cycle.(30'-60')

7) Transfer solution to a new well coated with streptavidin and capturethe biotinylated RNA that is also labeled with FITC. (15'-60')

8) Wash away excess FITC-NTP. (5'-15')

9) Read fluorescence. (10')

Example 8

As illustrated in FIG. 4, background may be reduced using restrictionenzyme digestion. A suitable procedure for carrying out this techniqueinvolves the following process steps:

1) Immobilize target to a solid phase.

2) Hybridize Probe A to target. Wash away excess Probe A.

3) Add restriction enzyme and reaction buffer.

4) Incubate in order to cut DNA.

5) Continue with amplification, following the steps shown in Examples 1,2, or 3.

Example 9

As shown in FIG. 5, background may also be reduced by denaturation ofthe specifically bound probe. A suitable procedure for carrying out thistechnique involves the following process steps:

1) Immobilize target to a solid phase.

2) Hybridize Probe A to target. Wash away excess Probe A.

3) Denature, e.g., by heating the solution or by adding alkali.

4) Separate soluble material from the solid phase, e.g., by filtrationor centrifugation.

5) Continue with amplification, following the steps shown in Examples 1or 2.

Example 10

Target nucleic acid sequences may also be detected using a probe asshown in FIG. 6. The process steps follow are described in Examples 1,2, or 3.

While this invention has been described with an emphasis upon preferredembodiments, it will be obvious to those of ordinary skill in the artthat variations in the preferred processes and kits may be used and thatit is intended that the invention may be practiced otherwise than asspecifically described herein. Accordingly, this invention includes allmodifications encompassed within the spirit and scope of the followingclaims.

What is claimed is:
 1. A nucleic acid-antibody construct, said constructcomprising:(a) a nucleic acid molecule comprising an RNA polymerasebinding site and a region that is transcribable into RNA; and (b) anantibody.
 2. A nucleic acid-antibody construct of claim 1, saidconstruct further comprising an RNA polymerase bound to the nucleic acidmolecule.
 3. A nucleic acid molecule-antibody construct of claim 1, saidconstruct further comprising an antigen bound to the antibody of thenucleic acid-antibody construct.
 4. A nucleic acid-antibody construct ofclaim 3, said construct further comprising an RNA polymerase bound tothe nucleic acid molecule.
 5. A process of detecting an antigen, saidprocess comprising the steps of:(1) binding a nucleic acid-antibodyconstruct to an antigen, said construct comprising a nucleic acidmolecule and an antibody, so as to form a nucleic acid-antibody-antigenconstruct, said nucleic acid molecule comprising an RNA polymerasebinding site and a region transcribable into RNA; (2) binding an RNApolymerase to said RNA polymerase binding site so as to result in thetranscription of RNA from the region transcribable into RNA; and (3)detecting the RNA as an indication of the presence of the antigen beingbound to the nucleic acid-antibody construct.
 6. A process of claim 5wherein the nucleic acid-antibody-antigen construct is bound to a solidsupport so as to permit the removal of nucleic acid molecule-antibodyconstruct that is not bound to said support.